The invention disclosed herein is generally related to heaters and temperature controllers for fluids. More particularly, this invention is related to feedback controlled heaters and temperature regulators for flowing liquids. This invention is the result of a contract with the U.S. Department of Energy (Contract No. W-7405-ENG-36).
The present invention was developed to meet a need for a temperature controller capable of maintaining a circulating stream of liquid at a constant temperature. The particular need was for an experimental heat engine which must be heated or cooled with a stream of water which is maintained at a substantially constant temperature. It will be recognized however that there are various other applications in which there is required a stream of water heated to a constant temperature.
Common electrical resistive heating devices suffer from certain disadvantages. For example, they must be provided with electrical feedthroughs into the fluid stream. Also, they must be insulated with insulation that can withstand prolonged exposure to fluid, typically water, at an elevated temperature. Such insulation necessarily decreases the efficiency and speed of heat transfer to the fluid. A key problem, however, is how to drive such a heater. A phase controlled SCR could be used, but it would generate noise from 60 Hz to approximately one MHz and, at the power levels required, shielding would be difficult because of the low frequency components. A preferred way would be to use a switching-regulated power supply, so that low-frequency noise would be eliminated. With modern FET power transistors, two semiconductors would be able to accommodate up to 10 kilowatts at 200 kHz. However, such a power supply, coupled to a resistive heater, would still suffer from the disadvantages of the use of feedthroughs, insulation and the noise problem mentioned above.
Accordingly, it is the object and purpose of the present invention to provide a regulated heater for heating a flowing stream of liquid, which is subject to temperature fluctuations, to a predetermined desired temperature.
It is also an object of the present invention to provide a feedback regulated heater which can efficiently apply large amounts of heat, within a short response time, to a flowing fluid which is subject to rapid temperature fluctuations so as to maintain the fluid at a substantially constant temperature.
It is another object of the invention to provide such a heater in which the active heating element has a low heat capacity and is free of electrical insulation, leads and feedthroughs.